Moistureproof pellicles and method of making them



nited States Patent Leo J. Novak and Joseph T. Tyree, Dayton, Ohio, as-

signors to The Commonwealth Engineering Company of Ohio, Dayton, Ohio, a corporation of Ohio No Drawing. Application May 6, 1958, Serial No. 353,440

18 Claims. (Cl. 117-144) This invention relates to improvements in the manufacture of sheets, films or pellicles especially suitable for use as a wrapping tissue.

It is essential to the manufacturers and vendors thereof that their various products, such as foodstuffs, drugs, candy, vegetables, tobacco products and the like, reach the consumer in their initial fresh condition, and therefore it is desirable to provide such products with a wrapping which is resistant to the passage of moisture.

Wax paper was used for many years as wrapping for the aforementioned purpose. It was recognized as less than satisfactory, however, since it is opaque whereas the preference is for a transparent wrapping material which makes for an attractive package and exposes the contents. Also, many waxed papers have an objectionable tendency to be, or to become greasy, and are, in addition, lacking in flexibility so that they crack on folding or creasing.

More recently there has been available as wrapping material a product comprising a regenerated cellulose (cellophane) base carrying a thin coating of a moistureproofing wax composition. The wax-coated cellophane is not useful as a general, all-purpose moisture-proof wrapping material. Thus, it has been found that when such sheets are used for packaging moist or wet materials of the type of butter, cheese and the like, the coating comprising the wax becomes detached or loosened from the base rather readily, the loosening taking place in less than an hour when the wrapping is in actual contact with water.

Various attempts have been made to circumvent this dilficulty. For example, it has been proposed to provide the regenerated cellulose with a coating comprising a combination of wax and a cellulose derivative or rubber, or to utilize an intermediate film of a so-called anchoring agent for increasing the adherence of the moistureproofing top coating to the base.

The object of the present invention is to provide strong, flexible, water-repellent sheet material capable of resisting the passage of water, either liquid or vapor, therethrough to a substantial extent if not completely, and for long periods of time. Another object is to provide a sheet material carrying a moisture-proofing coating which is not easily detached or loosened from the base sheet material even when it is exposed to direct contact with water for many hours. Still another object is to provide a new water-proof sheet material. A further object is to provide water-proof cellophane which does not depend for its resistance to water on nitrocellulose lacquers.

The objects of this invention are accomplished by coating the film or pellicle, such as regenerated cellulose film, with an ester of a dextran with a fatty acid containing from 8 to 18, preferably from 12 or 14 to 18, carbon atoms.

The dextrans are high molecular weight, branched polysaccharides made up of anhydroglucopyranosidic units joined by linkages some of which are alpha-1,6 linkages and some of which are alpha-non-1,6 linkages and at least 50% of these linkages being, apparently, of the alpha- 2,766,143 Patented Oct. 9,1956

1,6 type. The properties of the dextrans, including the molecular weight, the extent of branching (the number and distribution of side groups or chains), the molecular structural repeating alpha-1,6 to alpha-non-1,6 linkages ratios, and the water sensitivity vary.

The dextrans may be obtained in various ways. For example, they may be produced bacterially by inoculating; a nutrient medium containing sucrose, particular nitrogenous compounds and certain inorganic salts with an appropriate microorganism, such as those of the Leuconostoc mesenteroz'des and L. dextranicum types and incubating the culture at the temperature most favorable to the growth of the particular microorganism.

In one method of obtaining a dextran to be esterified to produce the moistureproofing agents of the invention, there is first prepared an aqueous nutrient medium which may have the following composition:

Percent by weight Sucrose 20.0 Corn steep liquor 3.0 Monobasic potassium phosphate 0.5 Manganous sulfate 0.002 Sodium chloride 0.50 Water Balance This medium is adjusted to a pH of between about 6.5 and about 7.5 preferably 7.2, and then sterilized. The material is cooled to room temperature and inoculated with a culture of the dextran-producing bacteria, for instance, Leuconostoc mesenteroides B5l2 (Northern Regional Research Laboratory classification) and incubated at 20 to 30 C. (optimum 25 C.) until a maximum yield of dextran has been attained; normally a period of between 12 and 48 hours will be satisfactory for this procedure. The fermented product contains approximately -85% of water and is a thick turbid liquid.

Upon completion of the fermentation, which process renders the material somewhat acid, that is, to a pH of 3.5-5.5 (average 4.2), calcium chloride is added to the ferment to bring the pH thereof to about 7.0 to 8.0. This aids in the precipitation of phosphates. Thereafter, acetone or alcohol, which may be a water-miscible aliphatic, such as methyl, ethyl or isopropyl, is added in sufficient quantity to precipitate the dextran and this brings down, with the dextran, occluded and adsorbed bacteria, and nitrogenous and inorganic elements. To occasion complete precipitation of the dextran it may be desirable to allow the mix to stand for a relatively long period, such as about 6 hours. The precipitated dextran may be dried in any suitable manner, for example by drum drying. Thereafter, it may be reduced to particulate condition.

A purer dextran may be obtained by adding an aliphatic alcohol to the fermented culture at a pH between about 2.5 and 4.5. The precipitate thus obtained may be further purified by again precipitating it with the alcohol. Several precipitations may be performed.

The dextran thus produced is a so-called native dextran having a high molecular weight and being, in the particular case, soluble in water at ordinary temperatures.

The higher fatty acid radicals may be introduced into the molecule of dextrans having molecular weights of from 5,000 to 50 10 as determined by light scattering measurements, to obtain the moistureproofing agents of this invention. For example, the fatty acid radicals may be introduced into the molecule of high molecular weight dextrans such as the native" product obtained as described above or an equivalent dextran, or such dextrans of high molecular weight may be hydrolyzed to lower molecular weight products prior to introduction of the fatty acid radicals, the hydrolysis being effected in any suitable manner, as by means of acid or enzymatically,

and. followed or not by a fractionation treatment for producing a fraction of uniform or more nearly uniform molecular weight, and by purification of the fraction for removal of pyrogens and coloring materials. While such refinements may be carried out in handling the dextran, prior to esterification thereof, they are optional and are not essential for the present purposes.

The dextran may be obtained by inoculating the culture medium with microorganisms other than that mentioned above. Thus it may be a water-soluble dextran obtained by the use of the microorganisms bearing the following NRRL classifications: Leuconostoc mesenteroides B-l19, B-1146, 3-1190, or a water-insoluble or substantially water-insoluble dextran obtained by the use of Leuconostoc mesenteroides B742, 13-1191, B-1196, B1208, B12l6, 13-1120, B-1144, 8-523, Streptobacterium dextranicum 13-1254 and Betabacterium vermiforme B-1139.

The dextran is not limited to one prepared under any particular set of conditions, including the microorganism used. It may be produced enzymatically, in the substantial absence of bacteria, by cultivating an appropriate microorganism, for example, Leuconostoc mesenteroides 13-512 to obtain a dextran-producing enzyme, separating the enzyme from the medium in which it is produced, and introducing the enzyme into a medium in which dextran is produced by the action of the enzyme. Also, the dextran may be obtained by bacterial conversion of 1,4 linkages of dextrin to 1,6 linkages of dextran. The inherently hydrophilic dextran may be initially soluble in water or insoluble or substantially insoluble therein.

The higher fatty acid radicals may be introduced into the dextran molecule by any appropriate methods, to produce the dextran fatty acid esters to be used in moistureproofing the regenerated cellulose or similar film. The ester may be prepared by the methods described in our pending application, Serial No. 351,743, filed April 28, 1953. Thus, the dextran, in the form of a free-flowing, white powder, may be reacted with an esterifying derivative of the higher fatty acid, and preferably a halide such as the chloride thereof, in the presence of an acid accepter or binding agent such as an organic base, as for instance a heterocyclic tertiary amine of the type of quinoline, pyridine, N-methyl morpholine, etc. and in the presence of a substance in which the reaction product is at least partially solvated, that is dissolved or swollen, as it is formed during the reaction, which results in the reaction mass being maintained in a highly swollen or dissolved state and thus insures substantially uniform, homogeneous reaction between the dextran and the esterifying agent. Substances which dissolve or swell the ester as it is formed are, for example, xylene, toluene, di-

oxane, etc. In general, the reaction may be carried out at temperatures between 100 C. and 155 C. for timeperiods varying inversely with the temperature between a half hour and three hours. The ester may be recovered from the crude reaction mixture by washing the latter with water to remove the hydrochloride of the organic base, removing the aqueous layer, adding a solvent for the ester to the residual mass, precipitating the solution into a non-solvent for the ester, such as a lower aliphatic alcohol, and filtering to obtain the ester.

Or the introduction of the higher fatty acid radicals into the dextran molecule may be effected by reacting the dextran with the selected acid in the presence of an impeller which may be the anhydride of a monohalogenated monobasic organic acid, e. g., monochloro acetic anhydride, and an esterification catalyst such as magnesiurn perchlorate at temperatures at which the reaction mixture remains in the liquid state, in general in the range between 50 C. and 100 C. and for a time varying inversely with the temperature betweenone-half hour and two hours. The ester may be isolated fromthe crude reaction mass by cooling themass, dissolving it in a solvent therefor, precipitating it into a non-solvent for the ester, and filtering the ester.

The higher fatty acids which may be used as esterification agent, in the free acid form or in the form of their chlorides, are those saturated acids containing from 8 to 18 carbon atoms and including caprylic, pelargonic, palmitic, margaric, and stearicacids, and the corresponding chlorides. Two or more of the substantially pure acids, or chlorides thereof, may be used, resulting in the production of mixed dextran esters. Or commercial acids, which comprise mixtures, may be used. For ex ample, commercial or technical grade stearic acid, which comprises a mixture ofzstearic and palmitic acids, yields dextran stearate-palmitate.

The D. 5. (degree of substitution or ratio of fatty acid radicals to anhydroglucopyranosidic units of the dextran), may vary between less than 1.0 to about 3.0. Such esters may be obtained using the fatty acid or its chloride in amounts varying between less than 1.0, e. g., 0.5 and 10.0 parts thereof by weight per part of dextran. Unlike the dextrans, which are inherently hydrophilic even when they are not soluble in water, the fatty acid esters are resistant to moisture to an extent which depends on the D. S. In general the higher the proportion of fatty. acid radicals per anhydroglucopyranosidic unit, the greater is the water-resistance of the ester, especially when the radicals are derived from fatty acids having the longer chains and higher carbon content. Those esters having an average D. S. between, say, 2.5 and about 3.0 are definitely hydrophobic and water-repelling, but a lower average D. S., for instance an average D. S. of 2.0, may be sufiicient to render the ester hydrophobic when the esterifying acid (or chloride) contains 12, or 14, to 18 carbon atoms. The hydrophobic or water-repelling esters are preferred for moistureproofing cellophane and the like in accordance with. the invention. These esters are soluble in organic solvents and particularly those of the non-polar type, such as the halogenated hydrocarbons, e. g. chloroform and carbon tetrachloride, the aromatic hydrocarbons, e. g., benzene, toluene, the xylenes, and the Freons (commercially available ehlorofluoro-methanes of the type of Freon 11, a trichloro-monofluoro-methane, and Freon 12, a dichloro-difluoromethane), and may be applied to the base from such solvents. Solutions of from 2% to 10% by weight or higher concentration may be used.

The following examples, will illustrate specific embodiments of the invention.

Example I An alkaline solution of sodium cellulose xanthate (viscose) is prepared and cast into a sulfuric acid coagulating and regenerating bath in conventional manner. The film-is withdrawn from the setting bath and passed, by meansof rollers, through the usual successive treating baths in which it is desulfurized, bleached and plasticized, after which it is dried.

The resulting film is moisture-proofed by coating it with a 5% chloroform solution of a dextran palmitate containing, per anhydroglucopyranosidic unit, an average of 2.9 palmitoyl radicals. The treated film is then dried at about 60 C. Initially, the coated film is opaque but, as the drying under heat proceeds, the film becomes clearand transparent.

The coated film is highly resistant to penetration by moisture over a substantial time period and can be immersed in water without loss of the moisture-proof effect.

Example II A regenerated cellulose pellicle is prepared as in Example I, and'the dried pellicle is moistureproofed by coatingit with a, 5% solution of a dextran stearate containing an average of 2.9 stearoylradicals per anhydroglucopyranosidic unit, and drying the coated film at about 50 C. a

The film coated with the dextran stearate is resistant to penetration by moisture for long periods of time.

It will be understood that other esters of the class designated can be substituted for the palmitate and stearate used in the examples, with similar results, and that the D. S. of the ester is selected so that it is waterresistant and organic solvent-soluble.

Although the invention has been described in detail in connection with the use of the higher fatty acid esters of dextran as the moistureproofing agent, it is within the scope of the invention to substitute for those esters, in whole or in part, water-resistant derivatives or conversion products of the dextrans containing both chemically bound radicals derived from the fatty acids of from 8 to 18 carbon atoms and other chemically bound substituents including, lower acyl groups derived from fatty acids of from 1 to 5 carbon atoms, alkyl groups such as those containing from 1 to 5 carbon atoms, e. g. methyl, ethyl, propyl etc., aralkyl groups, e. g. those containing a total of 7 to 10 carbon atoms and including benzyl radicals, carboxyalkyl groups such as those in which the alkyl portion contains from 1 to 5 carbon atoms and notably carboxymethyl, and hydroxyalkyl, especially hydroxyethyl. The fatty acid esters of the dextran conversion products may contain, on the average, from less than 1.0 to about 1.0 of the substituents other than the higher fatty acid radicals and not less than 2.0 of the higher fatty acid radicals per anhydroglucopyranosidic unit. The average ratio of higher fatty acid radicals to anhydroglucopyranosidic unit may be from 2.0:1 to about 2.8:1 in these dextran converversion products, the substituents and the D. S. being selected so that the final product is water-repellent and useful as a moistureproofing agent for the base comprising normally hydrophilic film-forming material.

The thickness of the moistureproofing coating applied to the base may be varied. For instance, when the compositions comprising the water-repellent acid esters of dextrans and their various conversion products are laid down in the form of a thin continuous, unbroken film applied uniformly as a coating to both sides of an approximately 0.0009 inch thick sheet of cellulose regenerated from viscose so that the total coating thickness does not exceed 0.0005 inch, there is obtained a coated sheet which is moisture-proof and from which the waterresisting film or coating does not readily separate even in contact with water.

The moisture-proofing coating may be applied to the base film by various well known apparatuses, and by brushing, spraying, dipping or continuous passage through a bath of the composition.

While the invention has been illustrated as applied to the moistureproofing of regenerated cellulose film, it is also applicable to other smooth, non-fibrous, non-porous sheets and films which require moisture proofing. The base may comprise cellulose ethers, such as alkyl, hydroxyalkyl, carboxyalkyl, xanthated alkyl, xanthated hydroxyalkyl and xanthated carboxyalkyl types, or it may comprise an unmodified or hydrophilic dextran, cellulose phthalic acid, and the like, as well as such non-cellulosic, Water sensitive film-forming substances as casein, gelatin, etc., or mixtures of hydrophilic film-forming materials, for example the film may be formed from a solution of a mixture of viscose and low-substituted cellulose ethers.

As moistureproofing agents for cellophane and the like, the higher fatty acid dextran esters have important advantages over the known moistureproofing lacquers which have been used for this purpose, particularly from the standpoint of simplicity. The known lacquers are complicated formulations made up of diflerent ingredients which must be used in balanced proportions, such as mixtures of nitrocellulose, resins, plasticizers, wax and, frequently, zinc stearate or the like, all of which must be used in controlled proportions in order to obtain a useful, flexible, moistureproof final film. While the hydrophobic fatty acid esters of the dextrans and conversion products may be formulated with other materials such as waxes, plasticizers of the type of dibutyl phthalate, nitrocellulose, natural and synthetic resins and the like substances which have been used conventionally in moistureproofing coating compositions for cellophane, such mixtures are not required in the practice of the invention. The simple treatment with the organic solvent solutions of the esters of the invention, followed by evaporation of the solvent, preferably with moderate heating or warming, renders the film moistureproof. The coated film is transparent, flexible and adapted to use as a wrapping material.

It will be understood that, while there have been described herein certain specific embodiments of the invention, it is not intended thereby to have it limited to or circumscribed by the specific details given in view of the fact that this invention is susceptible of various modifications and changes which come within the spirit and scope of this disclosure and of the appended claims.

We claim:

1. As a new article of manufacture, a smooth, nonfibrous film of normally hydrophilic film-forming material having adhered thereto and being moistureproofed by a coating comprising a water-resistant, organic solventsoluble ester of dextran with a saturated fatty acid of from 8 to 18 carbon atoms.

2. As a new article of manufacture, a smooth, nonfibrous film of normally hydrophilic film-forming material having adhered thereto and being moistureproofed by a coating comprising a water-resistant, organic solventsoluble ester of dextran with a saturated fatty acid of from 12 to 18 carbon atoms.

3. As a new article of manufacture, a smooth, nonfibrous film of normally hydrophilic film-forming material having adhered thereto and being moistureproofed by a coating comprising dextran palmitate containing an average of from about 2.0 to about 3.0 pahnitoyl radicals per anhydroglucopyranosidic unit of the dextran.

4. As a new article of manufacture, a smooth, non fibrous film of normally hydrophilic film-forming material having adhered thereto and being moistureproofed by a coating comprising dextran palmitate containing an average of about 2.9 palmitoyl radicals per anhydroglucopyranosidic unit of the dextran.

5. As a new article of manufacture, a smooth, nonfibrous film of a normally hydrophilic film-forming material having adhered thereto and being moistureproofed by a coating comprising dextran stearate containing an average of from about 2.0 to about 3.0 stearoyl radicals per anhydroglucopyranosidic unit of the dextran.

6. As a new article of manufacture, a smooth, nonfibrous film of normally hydrophilic film-forming material having adhered thereto and being moistureproofed by a coating comprising dextran stearate containing an average of about 2.9 stearate radicals per anhydroglycopyranosidic unit of the dextran.

7. As a new article of manufacture, a smooth, nonfibrous film of normally hydrophilic film-forming material having adhered thereto and being moistureproofed by a coating comprising a water-resistant, organic solventsoluble mixed ester of dextran with a saturated fatty acid of from 8 to 18 carbon atoms and a lower fatty acid of from 1 to 5 carbon atoms, said ester containing an average of from about 2.0 to about 2.9 of the higher fatty acid radicals per anhydroglucopyranosidic unit and an average of up to 1.0 per anhydroglucopyranosidic unit of the lower fatty acid radicals.

8. As a new article of manufacture, a smooth, nonfibrous film of normally hydrophilic film-forming material having adhered thereto and being moistureproofed by a coating comprising a water-resistant, organic solventsoluble mixed ester ether of dextran containing an average of from about 2.0 to about 2.9 of radicals derived from a saturated fatty acid'of from 8 to 18 carbon atoms per anhydroglucopyranosidic unit and an average of' up to 1.0 per anhydroglucopyranosidic unit of alkyl radicals containing from 1 to 5 carbon atoms.

9. As a new article of manufacture, a smooth, nonfibrous film of normally hydrophilic film-forming material having adhered thereto and being moistureproofed by a coating comprising a water-resistant, organic solventsoluble mixed ester ether of dextran containing an average of from about 2.0 to about 2.9 of radicals derived: from a saturated fatty acid of from 8 to 18 carbon atoms per anhydroglucopyranosidic unit and an average of up to 1.0 per anhydroglucopyranosidic unit of aralkyl radicals containing a total of 7 to carbon atoms.

10. As a new article of manufacture, asmooth, nonfibrous film of normally hydrophilic film-forming material having adhered thereto andbeing moistureproofed by a coating comprising a Water-resistant, organic solventsoluble mixed ester ether of dextran. containing an average of from about 2.0 to about 2.9 of radicals derived from a saturated fatty acid of from 8 to 18 carbon atoms per anhydroglucopyranosidic unit and an average of up to 1.0 per anhydroglucopyranosidic unit of carboxyalkyl radicals in which the alkyl portion contains from 1 to 5 carbon atoms.

11. As a new article of manufacture, a smooth, nonfibrous film of normally hydrophilic film-forming material having adhered thereto and being-moistureproofed by a coating comprising a Water-resistant, organic solventsoluble mixed ester ether of dextran ester 2.9 of radicals derived from a saturated fatty acid of from- 8 to 18 carbon atoms per anhydroglucopyranosidic unit and an average of up to 1.0 per anhydroglucopyranosidic unit of liydroxyalkyl radicals in which the alkyl portion contains from 1 to 5 carbon atoms.

12. As a new article of manufacture, a smooth, nonfibrous film of regenerated cellulose, having adhered thereto and being moistureproofed by a coating of a. dextran palmitate containing an average of about 2.9 palrnitoyl radicals per anhydroglucopyranosidic unit.

13. As a new article of manufacture, a smooth, nonfibrous film of regenerated cellulose having adheredthereto and being moistureproofed by a coating of a dextran 8 stearate containing an average of from about 2 ;0 to about 3.0 stearoyl radicals per anhydroglucopyranosidi'c unit.

14.. As a new article of manufacture, a' smooth, nonfibrous film of regenerated cellulose having adhered thereto and being moistureproofed by a coating of a dextran stearate. containing an average of'about 2,9 stearoyl radicals per anhydroglucopyranosidic unit.

15. As a new article of manufacture a smooth, nonfibrous film of normally hydrophilic film-forming material having-adhered thereto and being moistureproofed by a coating comprising a water-resistant, organic solventsoluble ester of dextran containing, initially, at least some free hydroxyl groups with a fatty acid of from 8' to 18 carbon atoms.

16. As a new article-of manufacture, a smooth, nonfibrous film of normally hydrophilic film-forming material having adhered thereto and being moistureproofed by a coating comprising a water-resistant, organic solventsoluble ester of dextran containing, initially, at least some freehydroxyl groups with a fatty acid of from 12 to 18 carbon atoms.

17. As a new article of manufacture, a smooth, nonfibrous film of regenerated cellulose having adhered theretoand being moistureproofed by a coating comprising a Water-resistant, organic solvent-soluble ester of dextran containing, initially, at least some free hydroxyl groups with a fatty acid of from 8 to 18 carbon atoms.

18. As a new article of manufacture, a smooth, nonfibrcus film of regenerated cellulose having adhered thereto and being moistureproofed by a coating comprising a water-resistant, organic solventasoluble ester of dextran containing, initially, at least some free hydroxyl groups with a fatty acid of from 12 to 18 carbon atoms.

References (Iited'in the file of this patent UNITED STATES PATENTS 2,344,179 Stahly Mar. 14, 1944 2,503,624 Luaces Apr. 11, 1950 FOREIGN PATENTS 544,346 GreattBritain of 1942 591,820 Great Britain of 1947 

1. AS A NEW ARTICLE OF MANUFACTURE, A SMOOTH, NONFIBROUS FILM OF NORMALLY HYDROPHILIC FILM-FORMING MATERIAL HAVING ADHERED THERETO AND BEING MOISTUREPROOFED BY A COATING COMPRISING A WATER-RESISTANT, ORGANIC SOLVENTSOLUBLE ESTER OF DEXTRAN WITH A SATURATED FATTY ACID OF FROM 8 TO 18 CARBON ATOMS. 